Complement Flashcards
How many complement proteins are their
Over 20
Which are concerned in biological activity sequence?
C1-9
What are the Complement factors
Factor B/D/Properdin
Complement Receptors
CR1/2/3
Is complement a pathway ?
Pathway oversimplification. Complement act like hub-like network tightly connected to other systems
3 main pathways
Activate same terminal sequence
C3—->C5—->C6—->C7—->C8—->C9
What’s is terminal sequence of 3 main Complement pathways
C3–>C5–>C6–>C7–>C8–>C9
What 3 main pathways
What are they activated by?
What is activation sequence?
Alternate pathway - activated by Ag/Ab complexes (IgM/IgG) -
C3–>B–>D–>P
Lectin pathway - activated by micro organisms - MBP–>C4–>C2
Classical pathway- activated by microorganism
C1–>C4–>C2
Complement cascade is enzymatic thus each enzyme can cleave many molecules of its substrate
Classical pathway is?
Activated by IgM, IgG
Many complement proteins have this Esther bonds which are very reactive with many Ag
C4b/C3b causes +ve feedback, able to cleave more C3—->C3b(+C3a)
Classical pathway sequence 1st step
- C1 binds FC region of Ab via C1q. Cross linking of multiple Ab must occur for proper change in C1q
Aids protection from host as Ag on pathogen is multimeric. Ag on host cells( glycoproteins) monomeric
Classical pathway sequence whole
- C1 binds Fc region of Ab via C1q
- C1r activates the proteinase C1s
- C1s cleaved C4 into C4b and C4a
- C4b binds the Ag, C4a remains in fluid phase
- C1s cleaves C2 to C2b and C2a
- C2b binds the Ag, C3a remains in fluid phase
- C4b/C2b forms C3 convertase, which cleaves C3 into C3b and C3a
- C3b binds the Ag, C3a remains in fluid phase
- C5 convertase (C4b/C2b/C3b) cleaves C5 to C5b and C5a. Where ends in gram +ve fungi as MAC can’t puncture thick cell walls
- C5b forms the MAC which causes lysis of gram-ve/helminths
